PROJECT SUMMARY Post-traumatic stress disorder (PTSD) is a debilitating psychiatric condition associated with high rates of chronicity, poor quality of life, and severe functional impairments. Treatments often include non-pharmacological and pharmacological interventions with variable success in improving symptoms. Gaining a better understanding of biological mechanisms related to changes in symptoms over the course of treatment is needed to develop future interventions as well as characterize biomarkers of response to help clinicians tailor drug and non-drug treatment strategies to individual patients. Our translational studies will utilize previously collected DNA from completed studies of meditation and group therapy for veterans with PTSD. Participants were assessed with clinical measures of symptom response longitudinally across multiple treatment time points. DNA from blood was collected before and after treatment. Using microarray technologies, we will examine how genetic polymorphisms and methylation predict treatment response and how methylation changes over time in relation to treatment response.